Hydrogen  ${(}_1{H}^1)$, Deuterium ${(}_1{H}^2)$ ,singly ionized Helium ${{(}_{2}H{e}^4)}^{+}$  and doubly ionized   ${{(}_{3}L{i}^6)}^{++}$  all have one electron around the nucleus. Consider an electron transition from  n=2 to n=1.If the wavelengths of emitted radiation are ${\lambda }_1,{\lambda }_2,{\lambda }_3$  and ${\lambda }_4$  respectively then approximately which one of the following is correct?